1. Field of the Invention
The subject invention relates to a method of making an alkoxylated polyethyleneimine product. More specifically, the subject invention relates to a method of treating a composition including at least one of a polyethyleneimine and an alkoxylated polyethyleneimine intermediate to improve the appearance of the alkoxylated polyethyleneimine product in an aqueous solution.
2. Description of the Related Art
Alkoxylated polyethylenimines (APEIs) are known in the art, as are methods of making APEI products including the APEIs. Among the APEIs, propoxylated polyethylenimines (PPEIs) and ethoxylated polyethylenimines (EPEIs) are most common in commercial applications. The EPEIs are commonly used in consumer products, especially laundry detergents, and generally function as dispersants by chelating cationic particles, such as clay particles, and holding them in solution. The EPEIs hold the particles in suspension until the particles are removed through a rinsing process, thus preventing the particles from re-depositing on the fabric in the laundry.
Current methods of making the APEI products start from a composition including polyethyleneimines (PEIs). A method of making the composition including the PEIs is by reacting ethylenediamine (EDA) and ethylenimine (EI) under acid catalysis, in solvents such as water. An example of a common EI is aziridine, which is a three-member ring having a reactive nitrogen. The EI is polymerized through a ring-opening reaction involving the reactive nitrogen of the aziridine. The reaction is maintained until the amount of unreacted EI falls below a predetermined level. The resulting polyethylenimines (PEIs) in the composition have primary, secondary, and tertiary amine functionalities that are available for further chemical conversion, e.g. alkoxylation with alkylene oxides such as ethylene oxide to form APEI. The ethoxylation of PEIs is described in Houben-Weyl, Methoden der organischen Chemie, 4. Ed., Vol. 14/2, p. 440 ff. (1963) and Vol. E 20, p. 1367 f. (1987).
One of the problems with current APEI products is discoloration in aqueous solutions including the APEI products. Incorporation of APEI products that cause significant discoloration in consumer products is undesirable since it can distort the desired color and appearance of the consumer products, which in turn can diminish consumer appeal. The discoloration of the aqueous solutions including the APEI products is typically measured using a UV-VIS spectrophotometer or by comparing the aqueous solutions including the APEI products to color standards such as Gardner color standards. In such measurements, the APEI products are diluted with solvents like water or alcohols, e.g. methanol or ethanol, THF, DMF or aqueous acids, to concentrations that are practical to determine coloristic properties. These concentrations can range from 5 to 30% by weight for the active polymer. Measurements of the coloristic properties are conducted at various wavelengths that can range from 350 to 800 nm and are carried out in one or two channel UV/Vis-spectrophotometers.
It is known in the art that impurities present in compositions including the PEI produce significant discoloration and high color in the aqueous solutions of APEI product made from them. However, there is no way of knowing from the appearance of the composition including the PEI whether aqueous solutions of APEI product with sufficiently low color can be made, since the compositions including the PEI are generally of low color, in the range of 1 to 3 by the Gardner standard.
Hydrides, such as sodium or potassium borohydride, are thought to improve the color of the aqueous solutions of APEI product and are often used in the manufacturing process. The aqueous solutions of APEI product manufactured following the conventional processes are highly colored and the formation of color bodies is unpredictable. For the aqueous solutions of APEI product manufactured following the conventional processes, Gardner color values are typically above 10 and often in the range of 14-18. Aqueous solutions of APEI product having Gardner color values greater than 10 are considered significantly discolored, and their utility in consumer products is inhibited. It is desirable to obtain aqueous solutions of APEI product with Gardner color values less than 6, which are presently unattainable through the use of the hydride or other measures alone.
U.S. Pat. No. 6,451,961 to Suzuki et al. suggests a method of treating compositions including PEI that have been produced from EI, which in turn was manufactured via a dehydration reaction of monoethanolamine in the presence of a catalyst. The method includes adding water to the PEI in an amount of from 1 to 95 parts water, based on the weight of the PEI to form the composition including the PEI. At least 15 percent of the added water is then distilled out of the composition at a temperature of from 212 to 392° F. and at reduced pressure to remove volatile impurities such as excess ethanolamine and other low-boiling residual components such as ammonia, lower alkyl amines, and aldehydes. According to the '961 patent, those volatile impurities cause offensive smell and a reduction in stability of the polyethyleneimines when present.
While it is obvious that water and other volatile compounds that are not chemically bound to the PEIs will be more quickly removed from the composition at higher temperatures, there could be factors that control the outcome of alkoxylation of the PEIs other than the removal of volatile impurities. Specific factors that may control the outcome of alkoxylation include the reaction of products of carbonyl compounds with the nitrogen functionality of the PEIs, subsequent removal of those products through distillation, and possible structural changes of the PEIs due to the removal of cross-linking building blocks. Such factors are not accounted for by the treatment method of the '961 patent. Furthermore, ethanolamine and ammonia, which are removed in the treatment method of the '961 patent, are not considered harmful in the sense of causing discoloration. More specifically, the functionalities of the ethanolamine and ammonia are also found in compositions including the PEI and/or the APEI product. Ethanolamine and ammonia are known to readily participate in the alkoxylation process, leading to colorless APEI products. Hence many of the volatile impurities removed in the '961 patent need not be removed to reduce discoloration of the aqueous solutions of APEI product, and the drawbacks of the presence of the ethanolamine and ammonia are not experienced by the consumer since the ethanolamine and ammonia are consumed during the production of the APEI product, thus yielding minute amounts of high molecular weight products in the APEI product that are chemically similar to the APEI. Finally, the presence of water in the composition including the PEI negatively affects alkoxylation beyond the reaction of one equivalent mole of alkylene oxide for each functionality of the PEI. As a result, the presence of excessive quantities of water during alkoxylation to produce the APEI product, which has more than one mole of alkylene oxide for each functionality of the PEI, is undesirable.
There remains an opportunity to provide a method of making APEI products that consistently exhibit improved color properties in aqueous solutions of the APEI products, namely Gardner color values of less than 6, without affecting the chemical structure or properties of the APEI products.